At present, a digital communication interface may be used to implement real-time detection, information report, on-line control, and program downloading of the microcontroller. A program debugging interface of a Silicon Labs C8051FXXX serial microcontroller is generally a C2 interface comprising a C2CK clock signal and a C2D bidirectional data signal.
A computer normally does not possess these digital interfaces itself. The currently used interfaces are only a serial port, a parallel port, and a universal serial bus (USB) interface. Most of laptop computers possess only the USB interface without the serial port. The USB interface is the most commonly used interface at present, and the feature of hot plugging enables the USB interface to present a prominent advantage in portability. In addition, the USB 2.0 interface reaches 480 Mbit/s in the theoretic transmission rate.
At present, the program downloader in the industry typically uses a conversion circuit between the USB and the serial port to connect the microcontroller first, then is converted into a inter-integrated circuit (I2C), a serial peripheral interface (SPI), or a joint test action group (JTAG) by using the microcontroller, and connects the download pen of the machine or several contact points by using cables in the exterior. However, peripheral devices are in a great quantity, and the reliability is poor, which brings inconveniences to portability and manufacture.